MYORISAN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MYORISAN (MYORISAN).
Isotretinoin, the active ingredient, reduces sebaceous gland size and sebum production, inhibits sebaceous gland differentiation, and has anti-inflammatory and immunomodulatory effects. It binds to retinoic acid receptors (RARs) and retinoid X receptors (RXRs), altering gene expression.
| Metabolism | Isotretinoin is highly protein-bound (>99.9%). It is metabolized in the liver primarily by CYP2C8, CYP2C9, CYP3A4, and CYP2B6. Major metabolites include 4-oxo-isotretinoin, tretinoin, and 4-oxo-tretinoin. Excretion is through urine and feces. |
| Excretion | Renal (approximately 60-80% as unchanged drug and minor metabolites) and biliary/fecal (approximately 20-30%, mostly as glucuronide conjugates). |
| Half-life | 14-20 hours (terminal elimination half-life in steady state; may be prolonged in elderly or renal impairment). |
| Protein binding | Approximately 99.9% bound to albumin; distributes to tissues including sebaceous glands. |
| Volume of Distribution | 1.3-2.1 L/kg (indicates extensive tissue distribution; accumulates in adipose tissue and skin). |
| Bioavailability | Oral: Approximately 25% (highly variable due to first-pass metabolism and food effect; absorption enhanced with high-fat meals). |
| Onset of Action | Oral: Clinical improvement in acne lesions typically observed within 4-8 weeks of continuous therapy. |
| Duration of Action | Acne remission may persist for several months to years after cessation of therapy; therapeutic effect decreases once drug is discontinued. |
| Molecular Weight | 300.44 |
Myorisan (isotretinoin) dosing: 0.5-1 mg/kg/day orally in two divided doses for 15-20 weeks.
| Dosage form | CAPSULE |
| Renal impairment | No dose adjustment recommended for renal impairment; caution in severe renal impairment due to possible accumulation. |
| Liver impairment | Contraindicated in patients with hepatic impairment (Child-Pugh class B and C). Use with caution and monitor LFTs in mild impairment. |
| Pediatric use | Pediatric use: Not recommended in children <12 years; for adolescents ≥12 years, dose per adult weight-based guidelines. |
| Geriatric use | No specific geriatric dose adjustment; caution due to potential for increased adverse effects (e.g., hypertriglyceridemia) and renal function decline. |
| 1st trimester | Contraindicated due to teratogenicity (major congenital malformations). |
| 2nd trimester | Contraindicated due to teratogenicity (major congenital malformations). |
| 3rd trimester | Contraindicated due to teratogenicity (major congenital malformations). |
Clinical note
Comprehensive clinical and safety monograph for MYORISAN (MYORISAN).
| Placental transfer | Crosses placenta; highly teratogenic. |
| Breastfeeding | Contraindicated during breastfeeding. Isotretinoin is excreted in human milk; potential for serious adverse effects in nursing infants. |
| Lactation Rating | L5 |
■ FDA Black Box Warning
Isotretinoin must not be used by female patients who are or may become pregnant. There is an extremely high risk of severe birth defects if pregnancy occurs while taking isotretinoin. Contraception is required. Also, isotretinoin is associated with inflammatory bowel disease.
| Serious Effects |
PregnancyWomen of childbearing potential without effective contraceptionBreastfeedingHypersensitivity to retinoidsElevated blood lipidsSevere hepatic or renal impairment
| Precautions | Pseudotumor cerebri (benign intracranial hypertension): risk increased with tetracycline use, Psychiatric disorders: depression, psychosis, suicidal ideation, Pancreatitis: serum triglycerides should be monitored, Hepatotoxicity: monitor liver function, Inflammatory bowel disease, Severe skin reactions (e.g., Stevens-Johnson syndrome), Photosensitivity, Hyperostosis with prolonged use, Ocular effects: dry eyes, corneal opacities, decreased night vision, Auditory impairment: tinnitus, hearing loss, Lipid abnormalities: hypertriglyceridemia, hypercholesterolemia, Allergic reactions, Skeletal muscle toxicity: rhabdomyolysis |
| Food/Dietary |
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| Teratogenic Risk | First trimester: Major congenital malformations (CNS, cardiovascular, facial dysmorphism) in up to 40% of exposed fetuses; Second trimester: CNS and growth abnormalities; Third trimester: Premature epiphyseal closure, cranial bone anomalies. |
| Fetal Monitoring | Pregnancy test prior to initiation and monthly during therapy; fetal ultrasound before, at 4-6 weeks, and at 16-20 weeks gestation; avoid supplementation with vitamin A. |
| Fertility Effects | Reversible impairment in spermatogenesis and ovulation in animal studies; human data limited but potential for reduced fertility. |
| Myorisan should be taken with a meal containing fat (e.g., full-fat milk, peanut butter) to enhance absorption. Avoid alcohol, as it may exacerbate hypertriglyceridemia. Avoid vitamin A supplements or foods high in vitamin A (e.g., liver). |
| Clinical Pearls | Myorisan (isotretinoin) is a retinoid indicated for severe recalcitrant nodular acne. Must be prescribed under the iPLEDGE program due to teratogenicity. Monitor for depression, suicidal ideation, and pseudotumor cerebri. Obtain baseline and monthly pregnancy tests in female patients of childbearing potential. Can cause elevated triglycerides and transaminases; monitor fasting lipids and LFTs monthly. Avoid concurrent tetracyclines due to increased risk of pseudotumor cerebri. Administer with food for optimal absorption. |
| Patient Advice | Do not get pregnant while taking Myorisan or for 1 month after stopping due to severe birth defects. · Two forms of contraception are required for female patients of childbearing potential, starting 1 month before treatment. · Do not donate blood during and for 1 month after treatment. · Report any mood changes, depression, or suicidal thoughts immediately. · May cause dry skin, lips, eyes, and nose; use moisturizers and lip balm. · Avoid waxing, dermabrasion, or laser treatments due to fragile skin. · Alcohol should be avoided or limited due to risk of elevated triglycerides. · Take with a meal containing fat to improve absorption. · Avoid vitamin A supplements to prevent toxicity. |